1. Field of the Invention
The present invention relates generally to an electron emission device, and more particularly to an electron emission display device which has a plurality of electron emission devices arranged in an image display array, for example, in a matrix form.
2. Description of the Related Art
Conventionally, in field electron emission display apparatuses, a Field Emission Display (FED) is known as a planar emission display device equipped with an array of cold cathode electron emission sources which does not require cathode heating. The emission principle of, for example, an FED using Spindt-type cold cathodes of minute protrusions is as follows. Its emission principle is like a Cathode Ray Tube (CRT), although this FED has a cathode array of Spindt-type protrusions which is different from that of CRT. In the FED, electrons are drawn into a vacuum space by means of each gate electrode spaced apart from the Spindt-type cathode, and the electrons are made to impinge upon the fluorescent substance that is coated on a transparent anode, thereby causing light emission.
This FED, however, has a problem of low production yield because the manufacture of the minute Spindt-type emitter arrays as a cold cathode is complex and involves many processes.
There is also known an electron emission device with electron emission devices of metal-insulator-metal (MIM) structure as a planar electron emission source. The electron emission device with the MIM structure comprises an Al underlayer as a base electrode, an Al.sub.2 O.sub.3 insulator layer with about 10 nm thickness, and a Au overlayer, as a top electrode with about 10 nm thickness which are formed in order on the substrate. In the case that this MIM device is placed under an opposing electrode in a vacuum, when a voltage is applied between the Al underlayer and the Au overlayer and, at the same time, an acceleration voltage is applied to the opposing electrode, then some of electrons emit out of the Au overlayer and reach the opposing electrode.
However, even the electron emission device with the MIM structure does not yet provide a sufficient amount of emitted electrons.
To overcome these disadvantages of emission of the MIM device, it is conventionally considered that there is a necessity to make the Al.sub.2 O.sub.3 insulator layer thinner by about several nanometers and make the Al.sub.2 O.sub.3 insulator layer with a uniform quality so that the interface between the Al.sub.2 O.sub.3 insulator layer and the Au overlayer is more uniform.
To provide a thinner and more uniform insulator layer, for example, an attempt has been made to control the anodized current by using an anodization method thereby to improve the electron emission characteristics, as in the invention described in Japanese Patent Application kokai No. Hei 7-65710.
However, even an electron emission device with the MIM structure which is manufactured by this anodization method ensures an emission current of about 1.times.10.sup.-5 A/cm.sup.2 and an electron emission efficiency of about 0.1%.
The MIM type electron emission device whose insulator layer has a thickness of several tens of nanometers to several micrometers does not have a plane forming status formed uniformly resulting in a problem of bringing an unstable electron emission property of the device.
A surface conductive type electron emission device is further known. This type device is manufactured as follows. First a pair of facing electrodes are formed on a substrate of an insulative material. Subsequently a conductive thin film is bridged between the facing electrodes. The conductive thin film bridge is electrified as an electrifying process so as to form a gap or break as an electron emission portion therein. Since such a gap or break is generated by locally destroying, denaturing or modifying the conductive thin film, there are problems in that the structural homogeneity in the electron emission portion is inferior and, the re-productivity in shape of the electron emission portion is very poor. The electron emission portion is restricted in shape within a linear line.